Conventional turbine engines used in most applications, including aviation, power generation, and industrial applications, generally have a combustion chamber, in which fuel is combusted in the presence of air to produce exhaust gas which drives a series of gears/shafts and ultimately the driven load (such as a propeller, fan or blades of the turbine engine, a pump, a generator, or a speed conversion unit) depending upon the application, and a continuous-stream fuel delivery system (such as a valve or nozzle), which delivers fuel to the combustion chamber for combustion. These fuel delivery systems generally introduce fuel in a continuous stream into the combustion chamber, and are usually controlled by mechanical means that sense and respond continuous stream into the combustion chamber, and are usually controlled by mechanical means that sense and respond to changing pressure, vacuum, or other physical or mechanical inputs within the system.
Conventional fuel delivery systems for turbine engines also rely on any of several physical processes to break the continuous fuel stream into fuel droplets or a mist for combustion to take advantage of the well-known inverse relationship between the size of a fuel droplet and the efficiency of combustion. The smaller the fuel particle, the greater the rate and efficiency of combustion. Engineers and scientists have experimented with fuel nozzle design for many years to maximize the efficiency of combustion. Examples include U.S. Pat. No. 5,603,211 (“Outer Shear Layer Swirl Mixer for a Combustor”) and U.S. Pat. No. 5,966,937 (“Radial Inlet Swirler with Twisted Vanes for Fuel Injector”). Typical “break-up” processes include the use of physical barriers against which fuel is directed to spatter it into droplets; the use of “swirlers,” “slingers” or other centrifugal force generators which sling fuel against the wall of a combustion chamber to break up a continuous fuel stream using mechanical means; and the use of high velocity air streams to fractionate a continuous fuel stream. Thus, the object of the modern design of turbine fuel delivery systems is to employ a process to break up a continuous stream of fuel droplets or to atomize the fuel. An object of this invention is to supplement the mechanical breakup of fuel by pulsing the fuel stream into the combustion chamber.
Turbine engines as described above suffer from several significant limitations that relate to continuous-stream, mechanical-control delivery systems. These limitations include at least the following: (1) fuel combustion is less efficient than it would be if fuel would be introduced into the combustion chamber in droplets rather than via a continuous stream; (2) there may be inefficient fuel distribution throughout the combustion chamber, which contributes to the inefficiency of combustion; (3) the exhaust gas often contains unburned fuel, which may contribute to air pollution; (4) the control systems often do not permit the operator control the fuel delivery process in relation to important operating variables (such as flow rate, air consumption rate, load changes, etc) as precisely as may be desired; (5) the systems can be difficult to operate and maintain; (6) the control system can be complex because of many moving parts; (7) the systems can add unwanted weight to the turbine, which is particularly problematic in aviation applications; and (8) the delivery and control systems can be expensive to manufacture and/or assemble because of their complexity and close mechanical tolerances; and (9) the response time is inherently slow because it is a mechanical system.
This invention is designed to overcome these limitations through two principal features. First, fuel is injected into the combustion chamber in pulses, using a fuel injector, rather than in a continuous-stream delivery system. This feature offers the distinct advantage of atomizing the fuel and delivering it in pulses into the combustion chamber in a fine mist or even a vapor, and thereby eliminates the need to employ a physical process to break up a continuous fuel stream. The fuel is combusted more efficiently because the invention reduces the size of the individual fuel cells that are being burned. Fuel injectors are commonly used for this purpose in internal combustion engines (see, e.g., U.S. Pat. No. 6,279,841 (“Fuel Injection Valve”) and U.S. Pat. No. 6,260,547 (“Apparatus and Method for Improving the Performance of a Motor Vehicle Internal Combustion Method”)) but have not been used to inject fuel pulses in turbine engines. Second, the invention uses an electronic control unit that detects sensor signals from chosen operating functions of the engine and then modifies the duration and/or frequency of fuel pulses that are injected into the combustion chamber. This control system thus provides precise operational control over a very broad range of operating conditions.
The combination of these features in the invention yields a fuel injection control system for a turbine engine that makes the engine more efficient, lighter, easier to operate and maintain, and more responsive than is currently available. In an aviation application, obviously any reduction in the weight of the turbine engine benefits the overall performance and fuel efficiency of the craft.